Synthesis and characterisation of group 11 metal complexes with a guanidine-tagged triphenylphosphine and evaluation of the isolated Au(I) complexes in gold-mediated organic reactions
Abstract
Phosphines bearing guanidine substituents at the backbone are attractive hybrid ligands that have not yet received adequate attention. This paper describes group 11 metal complexes of a guanidine-substituted triphenylphosphine, viz., N''-[2-(diphenylphosphino)phenyl]-N,N'-diisopropylguanidine (1).
Reactions of 1 with Cu(I) and Ag(I) precursors yielded the P,N-chelate complexes [M(1-κ2P,N)2]X, where M/X = Cu/BF4, Cu/Br, Ag/SbF6 and Ag/Br. Conversely, reacting 1 and the hydrochloride 1.HCl with [AuCl(SMe2)] produced the corresponding phosphine complexes [AuCl(1-κP)] and [AuCl(1H-κP)]Cl, which were further converted into [{μ(P,N)-1}2Au2][SbF6]2 and [AuCl(1H-κP)][SbF6], respectively, by reacting with Ag[SbF6].
These compounds and the bis-phosphine complex [Au(1-κP)2][SbF6] were studied as precatalysts in the Au-mediated cyclisation of N-propargylbenzamide and the addition of benzoic acid across terminal alkynes. Of the Au(I)-1 complexes studied, the complex [{μ(P,N)-1}2Au2][SbF6]2 was particularly attractive as a stable and well-defined, silver-free precatalyst, which can be conveniently activated in situ by the addition of a protic acid (either as an additive or a substrate).